The oomycete Phytophthora capsici Leonian is the causative agent of Phytophthora root rot, stem blight, and fruit rot in sweet bell pepper (Capsicum annuum). Phytophthora, sometimes also referred to as Phytophtora, is one of the most devastating diseases of peppers worldwide, potentially capable of causing large economic losses due to lower yields and/or damaged fruit. Breeding for Phytophthora resistant pepper plants is difficult due primarily to the existence of many different physiological races of the causative agent (Oelke et al., 2003, Glosier et al., 2007, Sy et al., 2008), the complex heritability of genetic resistance in the plant, and negative linkage drag of undesirable agronomic traits with the higher levels of genetic resistance available in unadapted germplasm.
Few good sources of resistance to Phytophthora are available in pepper. ‘Criollo de Morelos 334’ (‘CM334’), a perennial pepper, and ‘PI201234’, a plant introduction, have been described as having resistance, but these lines are exotic landraces with undesirable agronomic traits, such as having small pungent fruits. ‘CM334’ has the highest level of resistance against all known isolates of P. capsici. From this source, the number of Quantitative Trait Loci (QTL) explaining the resistance or tolerance to one race is estimated to vary between 2 QTLs (Minamiyama et al., 2007) up to 5-6 QTLs (Thabuis et al., 2003, Ogundiwin et al., 2005). While Marker Assisted Breeding (MAB) and recurrent selection programs have been used by pepper breeders in attempts to introgress the chromosomic fragments containing the resistant QTLs into sweet peppers, the resultant pepper lines lack the full resistance of the donor parent and/or fail to maintain certain desirable agronomic traits of the recurrent parent, such as the elite sweet blocky fruit preferred by producers and direct consumers of peppers (Thabuis et al., 2001, 2004). Thus, negative linkage drag and the difficulty of retaining multiple resistance QTLs in segregating progeny over generations of selection have inhibited the ability of breeders to develop elite, agronomically-acceptable bell pepper plants with the high levels of Phytophthora resistance desirable for commercial production.
The current invention provides new classes of elite sweet pepper lines with high levels of resistance to Phytophthora combined with highly desirable agronomic traits.